Criticism by police has rekindled debate about the so-called naked-body scanners as used by Amsterdam's Schiphol Airport, national media report.

The national police union, or GdP, has declared itself against their use. Body scanners that allow security personnel to see through clothing and the outlines of the body are an unacceptable compromise because "the private or intimate sphere of passengers should not be invaded," said GdP Chairman Konrad Freiberg.

Rainer Wendt, head of the police union, DPolG, said that security checks on passengers were "the most important interface when it came to ensuring air security." But the technology now used by police is insufficient, Wendt told the newspaper Berliner Zeitung. "We cannot labor under the illusion that security is free. Saving money here just tears holes in our security." Wendt also warned against outsourcing airport security because outside contractors might unknowingly employ terrorists.

Freiberg, too, warned against watering down security measures. It was just as important that the pressure is kept up on suspected terrorist cells. A potential terrorist should not be allowed to get as close to execution as in the attempt on Northwest Airlines flight 253 as it came into land in Detroit.

The failed bomber, Umar Farouk Abdulmutallab, 23, went through security checks at Amsterdam's Schiphol Airport when he transferred onto an Airbus A330. The attack was foiled by an alert Dutch passenger who confronted the man and wrestled him to the floor, overpowering him.

A report by Radio Netherlands Worldwide said that Dutch Anti-Terrorism Coordinator Erik Akerboom admitted that security checks are not watertight at Schiphol, which became one of the first international airports to introduce the body-scanning technology in May 2007.

Body scanners resemble shower cabins of plastic and Plexiglas. But unlike the more common X-ray-based scanners, body scanners use millimeter wave-reflection technology to produce an image of body contours as well as anything that might be strapped or connected to it such as fluids, metals, explosives and ceramic knives.

In a non-binding vote in 2008, the European Parliament voted down a plan to introduce body scanners at European airports, a report in the German daily newspaper Die Welt noted this week. Parliamentarians noted in 2008 that the scanners "have a serious impact on the fundamental rights of citizens" and asked the European Commission, the European Union's executive body, to investigate whether those rights would be violated by the devices.

The European debate over their use has focused on the apparently "crystal-clear images of the body contours," according to a report by the newspaper Welt Online in December last year. This means that "breasts, genitals, intimate piercings, love handles, amputations: all of it is plainly visible to the men and woman of the security service."

Welt Online reported that after the 2001 terror attacks in New York and Washington, the European Parliament bought eight body scanners at $100,000 each as part of its beefed-up security plan. But the scanners have never been installed and remain unused.

German airline Lufthansa has said that international passengers at Frankfurt, the country's largest international airport, should arrive at least three hours before their flight. German federal police, which looks after security at airports, said travelers bound for the United States would be put through additional security checks.